Introduce the NotificationDatabase class.

content/browser/notifications/notification_database.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_BROWSER_NOTIFICATIONS_NOTIFICATION_DATABASE_H_
+#define CONTENT_BROWSER_NOTIFICATIONS_NOTIFICATION_DATABASE_H_
+
+#include "base/callback.h"
+#include "base/files/file_path.h"
+#include "base/sequence_checker.h"
+#include "content/common/content_export.h"
+
+namespace leveldb {
+class DB;
+class Env;
+}
+
+namespace content {
+
+// Implementation of the persistent notification database.
+//
+// This class can be constructed on any thread, but method calls must only be
+// made on a thread or sequenced task runner that allows file I/O. The same
+// thread or task runner must be used for all method calls.
+class CONTENT_EXPORT NotificationDatabase {
+ public:
+  // Result status codes for interations with the database. Will be used for
+  // UMA, so the assigned ids must remain stable.
+  enum Status {
+    STATUS_OK = 0,
+
+    // The database, or the key associated with the operation, could not be
+    // found.
+    STATUS_ERROR_NOT_FOUND = 1,
+
+    // The database, or data in the database, could not be parsed as valid data.
+    STATUS_ERROR_CORRUPTED = 2,
+
+    // General failure code. More specific failures should be used if available.
+    STATUS_ERROR_FAILED = 3,
+  };
+
+  explicit NotificationDatabase(const base::FilePath& path);
+  ~NotificationDatabase();
+
+  // Opens the database. If |path| is non-empty, it will be created on the given
+  // directory on the filesystem. If |path| is empty, the database will be
+  // created in memory instead, and its lifetime will be tied to this instance.
+  // |create_if_missing| determines whether to create the database if necessary.
+  Status Open(bool create_if_missing);
+
+  // Completely destroys the contents of this database.
+  Status Destroy();
+
+ private:
+  friend class NotificationDatabaseTest;
+
+  // TODO(peter): Convert to an enum class when DCHECK_EQ supports this.
+  // See https://crbug.com/463869.
+  enum State {
+    STATE_UNINITIALIZED,
+    STATE_INITIALIZED,
+    STATE_DISABLED,
+  };
+
+  // Returns whether the database has been opened.
+  bool IsOpen() const { return db_ != nullptr; }
+
+  // Returns whether the database should only exist in memory.
+  bool IsInMemoryDatabase() const { return path_.empty(); }
+
+  base::FilePath path_;
+
+  // These members depend on the declaration order for destruction.

[Bernhard Bauer, 2015/03/11 21:35:11]

I would actually be explicit about it: |db_| depends on |env_|.

[Peter Beverloo, 2015/03/11 22:11:53]

Done.

+  scoped_ptr<leveldb::Env> env_;
+  scoped_ptr<leveldb::DB> db_;
+
+  State state_;
+
+  base::SequenceChecker sequence_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(NotificationDatabase);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_NOTIFICATIONS_NOTIFICATION_DATABASE_H_